A variety of approaches have been developed by railway vehicle brake system manufacturers, prior to the present invention, for railroad type braking systems in an attempt to control wheel slide as well as wheel lockup during a braking application. Most all of the present day adhesion adaptive, pattern recognition, wheel slide control processes use extremely complex digital logic arrangements in order to achieve the desired result.
These complex logic arrangements will quite often contain a number of variables and tables of variables. These variables and tables of variables are generally "setup" or "tuned" to each individual application. Actual field experience has demonstrated that this "tuning" process requires an individual who must be highly skilled in the art of railway wheel slide control design and application. In addition, this individual must possess a talent in the area of abstract reasoning. As would generally be expected, there are not a large number of individuals in this field who will possess all of these necessary qualifications.
Further difficulties experienced with these prior braking systems, which are presently known to applicants, include the possibility of their generating false signals indicating wheel slip.
One prior art type brake system which uses data from all of the axles disposed on the railway vehicle to determine wheel slide is taught in U.S. Pat. No. 4,071,282, issued Jan. 31, 1978 and entitled SLIP-SLIDE DETECTOR SYSTEM FOR RAILWAY CAR WHEELS. Although this brake system uses data from all the axles, it does not possess the capability of compensating for different wheel diameters. Such different wheel diameters may be caused, for example, by wear of the wheels. Thus, if the axles have different speeds, it may appear that a wheel slip is occurring, whereas in reality, the difference in axle speed may be due to differences in wheel diameter.
Additional background information regarding prior art wheel slippage control logic based on axle speed and acceleration rate is provided in U.S. Pat. No. 4,941,099, entitled "Adhesion Adaptive Wheel Slide Protection Process", which is, also, assigned to the assignee of the present invention.
Another method of detecting wheel slip and determining the severity of such wheel slip is described in the co-pending application, which was mentioned above: A METHOD OF AND APPARATUS FOR THE COMBINED DETECTION OF SPEED VARYING ENERGY LEVEL WHEEL SLIP DETECTION AND DETERMINATION OF WHEEL SLIP INTENSITY OF A RAILWAY VEHICLE BRAKE SYSTEM. This application bears Ser. No. 08/228,660 and was filed on Apr. 18, 1994, and is assigned to the assignee of the present invention. This invention forms a part of the present invention.
Another prior art method used for determining that a wheel slide has been corrected has been taught in U.S. Pat. No. 4,491,920, which is entitled "RATE POLARITY SHIFT WHEEL-SLIP CONTROL SYSTEM". This patent was issued on Jan. 1, 1985, and is, likewise, assigned to the assignee of the present invention.
This particular invention determines that a wheel slide condition has been corrected when the acceleration rate of an axle, which is sliding and being corrected, makes a transition from a positive to a negative acceleration rate.
The situation which is detected here is that of a wheel which has been sliding, and for which the braking force has been reduced. Reduction of the braking force allows the axle to accelerate and thereby approach the speed of the train, so its acceleration rate is positive. When such axle reaches the speed of the train, then its acceleration will become negative because the train, due to the braking, has a negative acceleration. At that point in time, since the wheel sliding has been corrected, the braking force on the axle is reapplied. This invention also forms a part of the present invention.
The teachings of each of U.S. Pat. Nos. 4,491,920, and 4,941,099 are incorporated herein by reference thereto.
The teachings of the patent application: A METHOD OF AND APPARATUS FOR THE COMBINED DETECTION OF SPEED VARYING ENERGY LEVEL WHEEL SLIP DETECTION AND DETERMINATION OF WHEEL SLIP INTENSITY OF A RAILWAYVEHICLE BRAKE SYSTEM, which is Ser. No. 08/228,660, filed on Apr. 18, 1994, and assigned to the assignee of the present invention, are also incorporated herein by reference thereto.
The teachings of the patent application: PROPORTIONAL POLARITY SHIFT WHEEL SLIDE PROTECTION, filed on May 8, 1995 and assigned Ser. No. 08/436,882, and assigned to the assignee of the present invention, are also incorporated herein by reference thereto.